A modern telecommunications device may support and implement many different network technologies. For example, a modern Customer Premises Equipment (CPE) is configured to communicate with User Equipment (UE) using Ethernet, Wireless Local Area Networks (WLAN, most commonly Wi-Fi as defined in the IEEE 802.11 family of standards) and cellular radio access technologies. CPEs which implement cellular radio access technology (such as the Long-Term Evolution (LTE) 4th Generation (4G) technology) are often known as small cells or Home eNodeBs, but may also be known as femtocells, picocells or microcells depending on their coverage area.
An example arrangement of two dwellings each served by their own CPE is shown in FIG. 1. As shown, each CPE includes a small cell (marked as “LTE”), a WLAN, a router and a DSL modem, either as part of the same device or communicatively attached. UEs within each house may communicate with their respective CPEs using either a wired Ethernet connection to the router, or wirelessly using either a cellular or WLAN communication method to the small cell or WLAN part of the CPE respectively. FIG. 1 illustrates two neighboring dwellings which are in close proximity with each other. Accordingly, the coverage areas of the small cell and WLAN parts of the CPEs (i.e. the areas covered by cellular or WLAN transmissions from the CPE) include the neighboring dwelling. It is therefore possible for a UE to be served by either CPE via cellular or WLAN access technologies so long as the UE has the correct access rights.
The CPE's Digital Subscriber Line (DSL) modem connects the CPE, and all UEs using that CPE, to the Core Network (including the network's Mobility Management Entity (MME) and Serving Gateway (S-GW) using the S1 interface) and external networks such as the Internet. This external connection is known as the backhaul. Each CPE's small cell may also communicate with neighboring small cells over the backhaul connection using the X2 interface. To set up an X2 connection between the two CPE's small cells, one small cell must determine the IP address of the other. This is typically accomplished in two stages. Firstly, the small cell determines identifying information of its neighboring small cells by either directly monitoring it through a Network Listen function, or by using an attached UE to report the presence of neighbors. These methods allow the small cell to determine the Cell Global Identifier (CGI) of neighboring CPEs, along with further measurements (such as signal strength). Once the small cell has determined which neighboring cell it wants to connect to, it requests the IP address of the neighboring cell from the MME over the S1 interface. The two small cells may then establish a connection over the X2 interface by transferring X2 setup messages.
Once two small cells are connected over the X2 interface, control plane traffic may be transferred between the two, which is typically used for fast transfer of handover information (such as when a UE disconnects from one CPE and connects to the other CPE), or for radio resource management. Data packets can also be forwarded over the X2 interface to bridge the delays in handover for non-real-time data. This X2 traffic is typically routed between the two small cells via an IPsec tunnel (in a similar manner to the tunnel used for the S1 interface).
In the event the CPE loses its backhaul connection, a large amount of functionality is lost. For example, the CPE, and all connected users, may no longer connect to external networks such as the Internet. This is true for both the cellular and WLAN access technologies. Furthermore, the CPE also cannot connect to other network elements, such as the S-GW or MME via the S1 interface, or other small cells via any existing X2 interfaces. It is also not possible for the CPE to establish any new X2 connections with any other small cells, as it is not possible for the CPE to establish the IP address without a backhaul connection to the MME. Thus, failure of the CPE's backhaul results in a frustrating period for the user during which they are stuck with a very limited service (typically just the routing functions of the CPE within its own network) until the backhaul is fixed.
It is therefore desirable to alleviate at least some of the above problems.